In a personal information terminal unit (hereinafter referred to as a “terminal”) such as a portable telephone, there is a relevant illicit use prevention method for preventing the use of a part or all of the functions for the terminal except for the authorized user in which the registered user is regarded as the authorized user, and if the unregistered user tries to use the terminal, the terminal is locked to prohibit the use.
One of the determination methods for the authorized user or the unauthorized user is a method of property authentication in which if the user possesses something registered beforehand other than the terminal, the user is regarded as authorized, or if not, the user is regarded as unauthorized.
An example of technique based on such method has been described in patent document 1. With this technique, a wristwatch is a device for the above purpose, each of the wristwatch and the terminal including a short distance wireless communication interface to enable the short distance wireless communication between the wristwatch and the terminal, and when the terminal can not receive a transmission packet transmitted regularly from the wristwatch, the terminal asks for a user authentication through the input of a password or biometric information, and performs a power off process if the authentication is unsuccessful, thereby preventing the illicit use.
However, with this technique, it is required that each the wristwatch and the terminal includes the short distance wireless communication interface dedicated for the above purpose, accordingly increasing the hardware and software, causing a demerit problem that the device is more expensive due to increased costs, has a larger size to limit the design, and is heavier in weight and hard to use.
In this way, since it is expensive to prepare the communication interface dedicated for the purpose of preventing the illicit use on both sides, a method using the existent communication is well known as a realistic solution strategy. As one example, the method relies on whether or not the user has a device such as a head set that may be used with the portable telephone as a pair. In patent document 2, for example, there is a technique for preventing the illicit use in which the terminal and the head set (device mounted on the head to hear sound by earphone) are connected through the normalized short distance wireless communication standards such as Bluetooth (BT) for transmitting or receiving a music signal or a music playback control signal, and its connection state is used for determination of the authorized use.
In this case, for example, the head set mounted on the head to hear music by earphone by transmitting music from the portable telephone through the BT connection may be diverted for determination of a lock timing, using a certain framework originally provided for other purposes, whereby there is an advantage that there is no problem of the cost up or increased size associated with the illicit use prevention.
Herein, a technique has been offered in which the head set is provided with a mounting detection part for detecting whether or not the head set 10 is mounted on the user, thereby automatically controlling the establishment and disconnection of wireless communication connection with a music playback device that is the partner of wireless communication depending on a use state of the head set, and the head set automatically disconnects the wireless connection with the music playback device through this process, when not in use, achieving power saving (e.g., refer to patent document 3).
Also, another technique has been offered in which the office equipment with a voice operation function of inputting a voice command or outputting a voice message through the head set as a device for voice input/output in which a microphone and a headphone connected to the unit main body are integrated includes an input signal detection part for detecting the presence or absence of a signal from the microphone of the head set at the start time of use and voice output means including a function of outputting a message of large volume or a buzzer sound from the headphone of the head set if there is no signal of this input signal detection part, whereby the visibility disabled person can use the head set efficiently (e.g., refer to patent document 4).
Also, another technique has been offered in which the portable terminal monitors the signal level of a short distance wireless signal from the wireless communication device to restrict the use of predetermined function for the portable terminal if this signal level falls below a level that the connection state of the short distance wireless communication can not be maintained, or to transfer the wireless communication function part of the portable terminal and the wireless communication device to a specific operation mode if the short distance wireless communication is not used over a predetermined time, and in the specific operation mode, the response speed of detecting a change in the signal level is decreased to delay issuing a request for increasing the transmission power to the wireless communication device, when the portable terminal monitors the signal level of a wireless signal from the wireless communication device, thereby reducing a variation in the operable distance between the portable terminal unit and the wireless communication device making the short distance wireless communication with this terminal unit beyond which the user is notified that the distance is larger or the use of the portable terminal unit is restricted (e.g., refer to patent document 5).
Also, another technique has been offered in which the portable telephone including short distance wireless communication means and a communication device capable of making the transaction with the short distance wireless communication means of the portable telephone are provided, the communication device including response signal transmitting means for transmitting a response signal to the portable telephone in response to an origination from the portable terminal, and the portable terminal including monitor signal originating means for originating a monitor signal to the communication device via the short distance wireless communication means in starting the operation of a predetermined function provided for the portable telephone and restricted in the operation and function restriction releasing means for releasing the restriction of the operation of the predetermined function in case of receiving a response signal transmitted from the communication device in accordance with the originated monitor signal, thereby suppressing the illicit use by the third party effectively while suppressing an operation load of the user (e.g., refer to patent document 6).
Also, another technique has been offered in which the head set periodically monitors a signal from the remote communication device in a sleep state, and if this signal is detected, the wireless head set transits to an active state, whereby the user can be provided with the functionality sufficient for the user (e.g., refer to patent document 7).    Patent document 1: Japanese Patent Laid Open Publication No. 2002-300651    Patent document 2: Japanese Patent Laid Open Publication No. 2004-102682    Patent document 3: Japanese Patent Laid Open Publication No. 2004-297256    Patent document 4: Japanese Patent Laid Open Publication No. 2005-236579    Patent document 5: Japanese Patent Laid Open Publication No. 2006-020226    Patent document 6: Japanese Patent Laid Open Publication No. 2006-033025    Patent document 7: Japanese Patent Laid Open Publication No. 2003-524341